Title of Invention	SORFC SYSTEM WITH NON-NOBLE METAL ELECTRODE COMPOSITIONS
Abstract	A solid oxide regenerative fuel cell and method of operation thereof are disclosed. The solid oxide regenerative fuel cell comprises a ceramic electrolyte, a first electrode which is adapted to be positively biased when the fuel cell operates in a fuel cell mode and in an electrolysis mode, and a second electrode which is adapted to be negatively biased when the fuel cell operates in the fuel cell mode and in the electrolysis mode. The second electrode comprises less than 1 mg/cm2 of noble metal.

Title of Invention

SORFC SYSTEM WITH NON-NOBLE METAL ELECTRODE COMPOSITIONS

Abstract

A solid oxide regenerative fuel cell and method of operation thereof are disclosed. The solid oxide regenerative fuel cell comprises a ceramic electrolyte, a first electrode which is adapted to be positively biased when the fuel cell operates in a fuel cell mode and in an electrolysis mode, and a second electrode which is adapted to be negatively biased when the fuel cell operates in the fuel cell mode and in the electrolysis mode. The second electrode comprises less than 1 mg/cm2 of noble metal.

Full Text	A SOLID OXIDE REGENERATIVE FUEL CELL AND METHOD OF OPERATION THEREOF BACKGROUND OF THE INVENTION [0001] The present invention is generally directed to a solid oxide regenerative fuel cell and method of operation thereof and more specifically to reversible fuel cells and their operation. [0002] Fuel cells are electrochemical devices which can convert energy stored in fuels to electrical energy with high efficiencies. There are classes of fuel cells that also allow reversed operation, such that oxidized fuel can be reduced back to unoxidized fuel using electrical energy as an input. [0003] One type of reversible or regenerative fuel cell is the solid oxide regenerative fuel cell (SORFC) which generates electrical energy and reactant product from fuel and oxidizer in a fuel cell or discharge mode and which generates the fuel and oxidant from the reactant product and the electrical energy in an electrolysis or charge mode. The SORFC contains a ceramic electrolyte, a positive or oxygen electrode and a negative or fuel electrode. The electrolyte may be yttria stabilized zirconia ("YSZ") or doped ceria. The positive electrode is exposed to an oxidizer, such as air, in the fuel cell mode and to a generated oxidant, such as oxygen gas, in the electrolysis mode. The positive electrode may be made of a ceramic material, such as lanthanum strontium manganite ("LSM") having a formula (La,Sr)MnO3 or lanthanum strontium cobaltite (LSCo) having a formula (La,Sr)CoO3. The negative electrode is exposed to a fuel, such as hydrogen gas, in a fuel cell mode and to water vapor (i.e., reactant product) in the electrolysis mode. Since the negative electrode is exposed to water vapor, it is made entirely of a noble metal or contains a large amount of noble metal which does not oxidize when exposed to water vapor. For example, the negative electrode may be made of platinum. [0004] However, the noble metals are expensive and increase the cost of the fuel cell. In contrast, the prior art acknowledges that the negative electrodes cannot be made from a non-noble metal in a SORFC because such electrodes are oxidized by the water vapor in the electrolysis mode. For example, an article by K. Eguchi et al. in Solid State Ionics 86-88 (1996) 1245-1249 states on page 1246 that a cell with Ni- YSZ electrodes is not suitable for a solid oxide electrolyzer cell. The article further states on page 1247 that that a high concentration of steam (i.e., water vapor) caused the deterioration of a Ni-YSZ electrode and that a noble or precious metal negative electrode is preferred. BRIEF SUMMARY OF THE INVENTION [0005] One preferred aspect of the present invention provides a solid oxide regenerative fuel cell, comprising a ceramic electrolyte, a first electrode which is adapted to be positively biased when the fuel cell operates in a fuel cell mode and in an electrolysis mode, and a second electrode which is adapted to be negatively biased when the fuel cell operates in the fuel cell mode and in the electrolysis mode. The second electrode comprises less than 1 mg/cm2 of noble metal. [0006] Another preferred aspect of the present invention provides a method of operating a solid oxide regenerative fuel cell, comprising operating the solid oxide regenerative fuel cell in a fuel cell mode by providing a fuel to a negative electrode and providing an oxidizer to a positive electrode to generate electricity and water vapor at the negative electrode. The method further comprises operating the solid oxide regenerative fuel cell in an electrolysis mode by providing electricity to the fuel cell and providing water vapor to the negative electrode to generate fuel at the negative electrode and oxygen at the positive electrode. The method further comprises providing a sufficient reducing atmosphere to the negative electrode when the solid oxide regenerative fuel cell operates in the electrolysis mode to prevent the negative electrode from oxidizing. The negative electrode comprises less than 1 mg/cm2 of noble metal. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS [0007] Figure 1 is a schematic illustration of a SORFC system operating in an electrolysis mode according to a preferred embodiment of the present invention. [0008] Figure 2 is a schematic illustration of a SORFC system operating in a fuel cell mode according to a preferred embodiment of the present invention. [0009] Figure 3 is a schematic cross section of a single SORFC operating in the electrolysis mode according to a preferred embodiment of the present invention. [0010] Figure 4 is a schematic cross section of a single SORFC operating in the fuel cell mode according to a preferred embodiment of the present invention. [0011] Figure 5 is a plot of current potential and power density versus current density of a SORFC cell according to a specific example of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT [0012] The present inventors have realized that SORFC negative (i.e., fuel) electrode may contain no noble metals or a small amount of noble metals, such as less than 1 mg/cm2 of noble metal, if a sufficient reducing atmosphere is provided to the negative electrode when the fuel cell operates in the electrolysis mode to prevent the negative electrode from oxidizing. The use of cheaper and/or more common conductive materials in the negative electrode reduces the cost of the SORFC and improves operational performance. [0013] As used herein, the term noble metal includes gold, iridium, palladium, platinum, rhodium, osmium and silver. These metals are also known as precious metals. Preferably, the negative electrode contains less than 20 weight percent of noble metal. More preferably, the negative electrode contains less than 0.1 mg/cm2 of noble metal and less than 1 weight percent of noble metal. Most preferably, the negative electrode contains no noble metal or an unavoidable trace impurity amount of noble metal. Furthermore, it is preferred that the positive electrode also contains no noble metal or an unavoidable trace impurity amount of noble metal. [0014] As used herein, the term SORFC (i.e., solid oxide regenerative fuel cell) includes a ceramic electrolyte, a positive or oxygen electrode which is adapted to be positively biased when the fuel cell operates in a fuel cell mode and in an electrolysis mode, and a negative or fuel electrode which is adapted to be negatively biased when the fuel cell operates in the fuel cell mode and in the electrolysis mode. Oxygen ions are conducted, through the ceramic electrolyte from the positive electrode to the negative electrode when the fuel cell operates in the fuel cell mode and from the negative electrode to the positive electrode when the fuel cell operates in the electrolysis mode. [0015] Any suitable materials may be used for the electrolyte and the electrodes. For example, the negative electrode may comprise a non-noble metal, such as at least one of Ni, Cu, Fe or a combination thereof with an ionic conducting phase (i.e., a cermet). In one preferred aspect of the invention, the negative electrode consists essentially of a Ni-YSZ cermet (i.e., a nickel-yttria stabilized zirconia cermet). Any suitable weight ratio of nickel to YSZ may be used in the electrode, such as a ratio of 30:70 to 95:5, preferably 65:35. The electrolyte may comprise any suitable ceramic, such as YSZ and/or doped ceria. [0016] In another preferred aspect of the invention, the negative electrode consists essentially of a Ni-doped ceria cermet. Any suitable weight ratio of nickel to doped ceria may be used in the electrode, such as a ratio of 30:70 to 95:5, preferably 65:35. In this case, the electrolyte preferably comprises a doped ceria electrolyte or a combination electrolyte having a doped ceria portion or layer in contact with the negative electrode and a YSZ portion in contact with the positive electrode. The ceria may be doped with any suitable dopant, such as a Sc dopant or a rare earth dopant selected from Gd and Sm, in an amount sufficient to render the ceria to be ionically conducting. [0017] The positive electrode may comprise any suitable material. Preferably, the positive electrode comprises a conductive perovskite ceramic material selected from LSM, LSCo, LCo, LSF, LSCoF, PSM or a combination thereof with an ionic conducting phase. Lanthanum strontium manganite ("LSM") preferably has a formula (Lax,Sr1-x) MnO3 where x ranges from 0.6 to 0.99, preferably from 0.8 to 0.85. Lanthanum strontium cobaltite ("LSCo") preferably has a formula (Lax,Sr1-x)CoO3 where x ranges from 0.6 to 0.99, preferably 0.8 to 0.85. If x is equal to one, then the electrode material comprises LCo. Lanthanum strontium ferrite ("LSF") preferably has a formula (Lax Sr1-x)FeO3 where x ranges from 0.4 to 0.99, preferably from 0.6 to 0.7. Lanthanum strontium cobalt ferrite ("LSCoF") preferably has a formula (Lax,Sr1-x)(Fey,Co1-y)O3 where x ranges from 0.4 to 0.99, preferably from 0.6 to 0.7 and y ranges from 0.01 to 0.99, preferably from 0.7 to 0.8. Praseodymium Strontium Manganite ("PSM") preferably has a formula (Prx,Sr1-x)MnO3 where x ranges from 0.6 to 0.99, preferably from 0.8 to 0.85. The perovskite electrode materials may optionally be admixed with the electrode ceramics, such as YSZ and doped ceria, such as GDC (gadolinium doped ceria). Other suitable pervoskite electrode materials may also be used. [0018] As used herein, "a sufficient reducing atmosphere to prevent the negative electrode from oxidizing" comprises any suitable reducing gas which when mixed with water vapor provided to the negative electrode during electrolysis mode prevents the negative electrode from oxidizing to an extent which prevents it from operating according to its designed parameters during its expected life span, such as for at least one month, preferably at least one year, such as one to ten years, for example. Preferably, hydrogen is used as the reducing gas. However, other gases, such as forming gas (a nitrogen/hydrogen mixture) and carbon monoxide may also be used alone or in combination with hydrogen. The maximum ratio of water vapor to reducing gas provided to the negative electrode during the electrolysis mode depends on the material of the negative electrode and on the type of reducing gas used. Some negative electrode materials require more reducing gas to prevent oxidation that other negative electrode materials. For example, if a hydrogen reducing gas is used for a Ni-YSZ electrode, then the water to hydrogen ratio is preferably 8 or less, for example 0.1 to 8, such as 0.4 to 5 or 0.44 to 1. However, the water to hydrogen ratio may be different than the ratio provided above depending on various factors, such as the electrode composition, the overall gas composition provided to the negative electrode and other factors, while still preventing the negative electrode from oxidizing to an extent which prevents it from operating according to its designed parameters during its expected life span. Preferably, the reducing atmosphere (i.e., the reducing gas) does not chemically participate in the electrolysis process and is cycled through the fuel cell without being consumed. [0019] Figure 1 illustrates a SORFC system 1 operating in the electrolysis or charge mode. The system 1 contains a schematically illustrated SORFC 10. While only a single SORFC 10 is shown, it should be understood that the system 1 preferably contains a stack of SORFCs, containing a plurality of electrolytes, positive electrodes and negative electrodes. The system 1 also contains a fuel storage vessel 101, such as a hydrogen tank, an optional fuel compressor 103, a water-hydrogen separator / water storage device 105, a water pump 107, an oxidizer blower 109, a fuel bleed valve 111 and optional water, oxidizer and compressor valves 113, 115 and 117, respectively. The system 1 also contains heat exchangers 119 and 121 which preheat the inlet streams into the fuel cell 10 using the fuel cell exhaust streams. The system further contains fuel and oxidizer conduits, such as pipes, hoses or other suitable gas and liquid conduits, which connect the above mentioned components together. [0020] The system contains a reducing gas conduit 123 which provides a sufficient reducing atmosphere to the negative electrode of the fuel cell 10 when the fuel cell operates in the electrolysis mode to prevent the negative electrode from oxidizing. Preferably, the reducing gas 123 conduit also comprises a fuel conduit which is used to provide fuel to the negative electrode during the fuel cell or discharge mode. Thus, the reducing gas in the electrolysis mode preferably, but not necessarily, comprises the same gas as the fuel which is used in the fuel cell mode. In the electrolysis mode, the bleed valve 111 located in the reducing gas conduit is partially opened to provide a smaller amount of fuel/reducing gas to the fuel cell than in the fuel cell mode. [0021] Preferably, the reducing gas/fuel comprises hydrogen and the reducing gas conduit 123 comprises a hydrogen conduit operatively connected to at least one of a hydrogen compressor 103 and the hydrogen fuel storage vessel 101. The term operatively connected means that the conduit 123 may be directly or indirectly connected to the compressor 103 and/or vessel 101 to allow hydrogen to flow from the compressor 103 and/or vessel 101 through the conduit 123 into the fuel cell. The conduit 123 is operatively connected to the fuel inlet of a fuel cell 10 (i.e., to the inlet of the fuel cell stack). [0022] The water-hydrogen separator 105 is also operatively connected to the fuel inlet of the fuel cell via the water inlet conduit 125. The separator 105 provides water to the negative electrode of the fuel cell 10 when the fuel cell 10 operates in the electrolysis mode. Preferably, the conduits 123 and 125 converge at the three way valve 113, and inlet conduit 127 provides the water and reducing gas from valve 113 to the negative electrode of the fuel cell 10. [0023] A fuel outlet of the fuel cell 10 is operatively connected to a water- hydrogen separator 105 via a fuel exhaust conduit 129. Conduit 129 removes water from the negative electrode when the fuel cell operates in the fuel cell mode. An oxygen exhaust conduit 131 removes oxygen generated at the positive electrode when the fuel cell operates in the electrolysis mode. An oxidizer inlet conduit 133 provides an oxidizer, such as air or oxygen, to the positive electrode of the fuel cell 10 when the fuel cell operates in the fuel cell mode. In the electrolysis mode, the conduit 133 is closed by valve 115. [0024] Figure 2 illustrates the SORFC system 1 operating in the fuel cell or discharge mode. The system 1 is the same, except that the bleed valve 111 is opened to a greater amount than in the electrolysis mode, the oxidizer valve 115 is open instead of closed and the water valve 113 either totally or partially closes the water conduit 125. [0025] A method of operating the solid oxide regenerative fuel cell system 1 will now be described. In the fuel cell mode shown in Figure 2, a fuel, such as hydrogen, carbon monoxide and/or a hydrocarbon gas, such as methane, is provided to the negative electrode of the fuel cell 10 from storage vessel 101 through conduits 123 and 127. The fuel is preheated in the heat exchanger 119. If desired, some water from the separator/storage device 105 is provided via conduits 125 and 127 to the negative electrode of the fuel cell as well. Alternatively, the water may be provided from a water pipe rather than from storage. [0026] An oxidizer, such as oxygen or air is provided to the positive electrode of the fuel cell 10 through conduit 133. This generates electricity (i.e., electrical energy) and water vapor at the negative electrode. The unused oxidizer is discharged through conduit 131. The water vapor reactant product along with unused fuel, such as hydrogen, and other gases, such as carbon monoxide, are discharged from the fuel cell through conduit 129 into the separator 105. The hydrogen is separated from water in the separator and is provided into the compressor 103 through conduit 135. The compressor 103 cycles the hydrogen back into the fuel cell 10. [0027] In the electrolysis mode shown in Figure 1, electricity is provided to the fuel cell. Water vapor is provided to the negative electrode of the fuel cell 10 from the separator/storage device 105 or from a water pipe through conduits 125 and 127. A sufficient reducing atmosphere, such as hydrogen gas, is also provided to the negative electrode through conduits 123 and 127. For example, at start-up of the SORFC operation, when the compressor 103 does not usually run, the hydrogen may be provided from the storage vessel 101. Subsequently, when the compressor 103 becomes operational at steady state, it provides hydrogen to the conduit 123 and to the storage vessel 101. [0028] This generates fuel, such as hydrogen, at the negative electrode, and oxygen at the positive electrode of the fuel cell. The hydrogen, including the hydrogen generated in the electrolysis of water vapor reaction and the hydrogen provided from conduit 123 along with remaining unreacted water vapor are provided from the fuel cell 10 through conduit 129 to the separator 105. The water-hydrogen separator 105 separates the hydrogen from water, with the water being either stored or discharged. The separated hydrogen is provided to the compressor 103 through conduit 135. The compressor provides a first portion of the compressed hydrogen to the hydrogen storage vessel 101 and provides a second portion of the compressed hydrogen to the negative electrode of the fuel cell 10 through conduit 125 to maintain the sufficient reducing atmosphere at the negative electrode. The oxygen generated during the electrolysis reaction is discharged through conduit 131. [0029] Preferably, the fuel cell 10 is cycled between the fuel cell mode and the electrolysis mode at least 30 times, such as 30 to 3,000 times. During the cycles, when the fuel cell operates in the electrolysis mode, the bleed valve 111 bleeds a first sufficient amount of hydrogen from at least one of the hydrogen compressor and the hydrogen fuel storage vessel through the hydrogen conduit 123 to the negative electrode of the fuel cell to prevent the negative electrode from oxidizing. Providing a reducing atmosphere on the negative electrode during the electrolysis mode allows the use of non-noble materials in the electrode which also maintains compatibility for the electrolysis operation. [0030] When the fuel cell operates in the fuel cell mode, the bleed valve provides hydrogen fuel from, the hydrogen storage vessel through the hydrogen conduit 123 to the negative electrode in a second amount greater than the first amount. In other words, the first amount of reducing gas should be a small amount of reducing gas, but sufficient to prevent oxidation of the negative electrode. [0031] It should be noted that the hydrogen conduit 123 provides a sufficient amount of reducing gas to the plurality of negative electrodes of a fuel cell stack to prevent all negative electrodes of the stack from oxidizing. Therefore the negative electrodes of the SORFC stack are maintained in a reducing atmosphere, preventing oxidation of the electrode materials at elevated temperatures in the range 600-1000°C. [0032] In alternative embodiments of the present invention, separate storage vessels are used to store fuel and the reducing gas. Preferably, this occurs when the fuel and reducing gas comprise different gases. For example, the fuel may comprise a hydrocarbon fuel rather than hydrogen, or forming gas or carbon monoxide is used as a reducing gas. In this case, a separate reducing gas storage vessel, such as a hydrogen, carbon monoxide or forming gas storage tank or pipe may be used to provide the reducing gas into the fuel cell 10 in the electrolysis mode, while the fuel storage vessel 101 is used to provide fuel into the fuel cell in the fuel cell mode. [0033] A single SORFC 10 operating in the electrolysis mode is shown in Figure 3. The SORFC contains an anode (positive) electrode 11, an electrolyte 13 and a cathode (negative) electrode 12. An anode gas chamber 14 is formed between the electrolyte 13 and an anode side interconnect (not shown for simplicity). A cathode gas chamber 15 is formed between the electrolyte 13 and a cathode side interconnect (also not shown for simplicity). [0034] A reaction product gas mixture 17 may contain primarily water with reducing gas, such as hydrogen. Alternatively, the reaction product gas mixture 17 may contain primarily water vapor and carbon dioxide if a carbon containing gas or liquid, such as methane, is used as a fuel. Hydrogen, carbon monoxide or forming gas is also added to the gas mixture as the reducing gas. [0035] The reaction product gas mixture 17 is introduced into the cathode gas chamber 15. A direct current power source (not shown) is connected to the anode electrode 11 and the cathode electrode 12 in such a way that when electrical current is flowing, the anode electrode 11 takes on a positive voltage charge and the cathode electrode 12 takes on a negative voltage charge. When the electric current is flowing, the gas mixture 17 gives up oxygen ions 16 to form cathode discharge mixture 19 consisting primarily of hydrogen and optionally carbon monoxide if mixture 17 contained carbon dioxide. Oxygen ions 16 transport across the electrolyte 13 under the electrical current. The oxygen ions 16 are converted into the oxidant, such as oxygen gas 18 on the anode electrode 11 under the influence of the electrical current. The oxygen gas 18 is discharged from the anode chamber 14, while the electrolysis product (e.g., hydrogen and optionally carbon monoxide) is collected from the cathode chamber. If carbon monoxide is present in the product, then the product may be converted to methane fuel and water in a Sabatier reactor. [0036] A single SORFC 20 operating in the fuel cell mode is shown in Fig. 4. SORFC 20 is the same as SORFC 10, except that the cathode and anode designations of its electrodes are reversed. Cathode (positive) electrode 21 is the same electrode as that identified as the anode (positive) electrode 11 in Fig. 3 when operating in the electrolysis mode. Anode (negative) electrode 22 is the same electrode as that identified as the cathode (negative) electrode 12 in Fig. 3 when operating in the electrolysis mode. Solid oxide electrolyte 23 is the same electrolyte as that identified as electrolyte 13 in Fig. 4 when operating in the electrolysis mode. Cathode gas chamber 24 is the same gas chamber as that identified as the "anode gas chamber 14 in Fig. 3 when operating in the electrolysis mode. Anode gas chamber 25 is the same gas chamber as that identified as the cathode gas chamber 15 in Fig. 3 when operating in the electrolysis mode. [0037] A fuel gas 27 is introduced into the anode gas chamber 25. An oxidizer, such as air or oxygen gas 28 is introduced into the cathode chamber 24. The fuel may comprise hydrogen, a hydrocarbon gas, such as methane, and/or carbon monoxide. Water may be added to the fuel if desired. An electrical fuel cell load (not shown) is applied to the SORFC 20 and the oxygen gas 28 forms oxygen ions 26 under the influence of the electrical load. Oxygen ions 26 transport across the electrolyte 23 under the influence of the electrical current. On the anode electrode 22, the oxygen ions 26 combine with hydrogen and optionally carbon, if present, from gas mixture 27 to form gas mixture 29 containing water vapor and optionally carbon dioxide, if a carbon containing gas is present in the fuel 27. Gas mixture 29 is discharged from the anode chamber and stored as the reaction product. In the process described above, the SORFC 20 has made electrical energy or power, which is output through its electrodes. [0038] The SORFC systems described herein may have other embodiments and configurations, as desired. Other components, such as fuel side exhaust stream condensers, heat exchangers, heat-driven heat pumps, turbines, additional gas separation devices, hydrogen separators which separate hydrogen from the fuel exhaust and provide hydrogen for external use, fuel preprocessing subsystems, fuel reformers, water-gas shift reactors, and Sabatier reactors which form methane from hydrogen and carbon monoxide, may be added if desired, as described, for example, in U.S. Application Serial Number 10/300,021, filed on November 20, 2002, in U.S. Provisional Application Serial Number 60/461,190, filed on April 9 2003, and in U.S. Application Serial Number 10/446,704, filed on May 29, 2003 all incorporated herein by reference in their entirety. [0039] The following specific example is provided for illustration only and should not be considered limiting on the scope of the present invention. Figure 5 illustrates the plot of cell potential and power density versus current density for a single 10 cm2 SORFC cell using a test bed that models the inlet gas streams as described with respect to Figures 1 and 2 above. The SORFC cell contains the following components. The negative or fuel electrode is a Ni-YSZ cermet electrode containing 65 weight percent Ni and 35 weight percent YSZ. This electrode is 27 microns thick and is made by screen printing on the electrolyte and being fired to 1350°C. The electrolyte is a YSZ electrolyte that is 300 microns thick. The electrolyte is tape cast and fired to 1550°C. The positive or oxygen electrode is an LSM electrode that is 39 microns thick. This electrode is made by screen printing on the electrolyte and firing to 1200°C. [0040] The negative electrode is fed with a constant 300 seem of H2 passing through a humidifier at a set temperature. The charge (i.e., electrolysis) mode is run with the humidifier set to 70°C or 30.75% H2O. This provides an H2O to H2 ratio of 0.44 to the negative electrode. One discharge (i.e., fuel cell) mode is run with the humidifier set to 70°C or 30.75% H2O, while another discharge (i.e., fuel cell) mode is run with the humidifier set to 29°C or 3.95% H2O. The H2O to H2 ratio is 0.44 and 0.04, respectively, for the respective discharge mode runs. Table 1 below lists the negative electrode conditions for the various modes of operation with ambient pressure reactants. [0041] As shown in Figure 5, this fuel cell with a negative electrode which contains no noble metal is successfully operated in both charge and discharge modes and exhibits acceptable current-voltage and current-power characteristics for reversible operation. [0042] The foregoing description of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The description was chosen in order to explain the principles of the invention and its practical application. It is intended that the scope of the invention be defined by the claims appended hereto, and their equivalents. WE CLAIM: 1. A solid oxide regenerative fuel cell, comprising: a ceramic electrolyte; a first electrode which is adapted to be positively biased when the fuel cell operates in a fuel cell mode and in an electrolysis mode; and a second electrode which is adapted to be negatively biased when the fuel cell operates in the fuel cell mode and in the electrolysis mode, characterized in that: the second electrode comprises less than 1 mg/cm2 of noble metal. 2. The fuel cell as claimed in claim 1, wherein the second electrode comprises less than 20 weight percent of noble metal. 3. The fuel cell as claimed in claim 2, wherein the second electrode comprises less than 0.1mg/cm2 of noble metal and less than 1 weight percent of noble metal. 4. The fuel cell as claimed in claim 3, wherein the second electrode comprises no noble metal or an unavoidable trace impurity amount of noble metal. 5. The fuel cell as claimed in claim 3, comprising a first device which is adapted to provide a sufficient reducing atmosphere to the second electrode when the fuel cell operates in the electrolysis mode to prevent the second electrode from oxidizing. 6. The fuel cell as claimed in claim 5, wherein the first device comprises a hydrogen conduit operatively connected to at least one of a hydrogen compressor and a hydrogen fuel storage vessel. 7. The fuel cell as claimed in claim 6, wherein the hydrogen conduit is operatively connected to a fuel inlet of a fuel cell stack and a fuel outlet of the fuel cell stack is operatively connected to a water-hydrogen separator. 8. The fuel cell as claimed in claim 7, wherein the water-hydrogen separator is operatively connected to the fuel inlet of the fuel cell stack and is adapted to provide water to the second electrode when the fuel cell operates in the electrolysis mode. 9. The fuel cell as claimed in claim 6, comprising a valve which is adapted to bleed a first sufficient amount of hydrogen from at least one of the hydrogen compressor and the hydrogen fuel storage vessel through the hydrogen conduit to the second electrode to prevent the second electrode from oxidizing when the fuel cell operates in the electrolysis mode and which is adapted to provide hydrogen fuel from the hydrogen storage vessel through the hydrogen conduit to the second electrode in a second amount greater than the first amount when the fuel cell operates in the fuel cell mode. 10. The fuel cell as claimed in claim 6, wherein the first device comprises a forming gas conduit operatively connected to a forming gas storage vessel. 11. The fuel cell as claimed in claim 6, wherein the first device comprises a carbon monoxide conduit operatively connected to a carbon monoxide storage vessel. 12. The fuel cell as claimed in claim 1, comprising a first means for providing a sufficient reducing atmosphere to the second electrode when the fuel cell operates in the electrolysis mode to prevent the second electrode from oxidizing. 13. The fuel cell as claimed in claim 12, wherein the first means is a means for providing hydrogen fuel to the second electrode when the fuel cell operates in the fuel cell mode. 14. The fuel cell as claimed in claim 13, comprising: a second means for providing water to the second electrode when the fuel cell operates in the electrolysis mode; a third means for removing oxygen generated at the first electrode when the fuel cell operates in the electrolysis mode; a fourth means for providing an oxidizer to the first electrode when the fuel cell operates in the fuel cell mode; and a fifth means for removing water from the second electrode when the fuel cell operates in the fuel cell mode. 15. The fuel cell as claimed in claim 5, wherein the second electrode comprises at least one of Ni, Cu, Fe or a combination thereof with an ionic conducting phase. 16. The fuel cell as claimed in claim 15, wherein the second electrode consists essentially of a Ni-YSZ cermet. 17. The fuel cell as claimed in claim 15, wherein: the second electrode consists essentially of a Ni-doped ceria cermet; and the electrolyte comprises a doped ceria portion in contact with the second electrode and a YSZ portion in contact with the first electrode. 18. The fuel cell as claimed in claim 15, wherein: the electrolyte comprises YSZ, doped ceria or a combination thereof; and the first electrode comprises at least one of LSM (lanthanum strontium manganite), LSCo (lanthanum strontium cobaltite), LCo (lanthanum cobaltite), LSF (lanthanum strontium ferrite), LSCoF (lanthanum strontium cobalt ferrite), PSM (praseodymium strontium manganite) or a combination thereof with an ionic conducting phase. 19. A solid oxide regenerative fuel cell, comprising: a first electrode which is adapted to be positively biased when the fuel cell operates in a fuel cell mode and in an electrolysis mode; a second electrode which is adapted to be negatively biased when the fuel cell operates in the fuel cell mode and in the electrolysis mode, characterized in that the second electrode comprises less than 1 mg/cm2 of noble metal; and a first means such as herein described for conducting oxygen ions from the first electrode to the second electrode when the fuel cell operates in the fuel cell mode and for conducting oxygen ions from the second electrode to the first electrode when the fuel cell operates in the electrolysis mode. 20. The fuel cell as claimed in claim 19, wherein the second electrode comprises less than 20 weight percent of noble metal. 21. The fuel cell as claimed in claim 20, wherein the second electrode comprises less than 0.1 mg/cm2 of noble metal and less than 1 weight percent of noble metal. 22. The fuel cell as claimed in claim 21, wherein the second electrode comprises no noble metal or an unavoidable trace impurity amount of noble metal. 23. The fuel cell as claimed in claim 19, comprising a second means such as herein described for providing a sufficient reducing atmosphere to the second electrode when the fuel cell operates in the electrolysis mode to prevent the second electrode from oxidizing. 24. The fuel cell as claimed in claim 23, wherein the second means is a means for providing hydrogen fuel to the second electrode when the fuel cell operates in the fuel cell mode. 25. The fuel cell as claimed in claim 24, comprising: a third means such as herein described for providing water to the second electrode when the fuel cell operates in the electrolysis mode; a fourth means such as herein described for removing oxygen generated at the first electrode when the fuel cell operates in the electrolysis mode; a fifth means such as herein described for providing an oxidizer to the first electrode when the fuel cell operates in the fuel cell mode; and a sixth means such as herein described for removing water from the second electrode when the fuel cell operates in the fuel cell mode. 26. The fuel cell as claimed in claim 19, wherein: the first electrode comprises at least one of LSM, LSCo, LCo, LSF, LSCoF, PSM or a combination thereof with an ionic conducting phase; and the second electrode comprises at least one of Ni, Cu, Fe or a combination thereof with an ionic conducting phase. 27. The fuel cell as claimed in claim 26, wherein: the first electrode consists essentially of LSM; and the second electrode consists essentially of a Ni-YSZ cermet. 28. A solid oxide regenerative fuel cell, comprising: a first electrode which is adapted to be positively biased when the fuel cell operates in a fuel cell mode and in an electrolysis mode; a second electrode which is adapted to be negatively biased when the fuel cell operates in the fuel cell mode and in the electrolysis mode, characterized in that the second electrode comprises less than 1 mg/cm2 of noble metal; a first means such as herein described such as herein described for conducting oxygen ions from the first electrode to the second electrode when the fuel cell operates in the fuel cell mode and for conducting oxygen ions from the second electrode to the first electrode when the fuel cell operates in the electrolysis mode; and a second means such as herein described for providing a sufficient reducing atmosphere to the second electrode when the fuel cell operates in the electrolysis mode to prevent the second electrode from oxidizing. 29. The fuel cell as claimed in claim 28, wherein the second electrode comprises less than 20 weight percent of noble metal. 30. The fuel cell as claimed in claim 29, wherein the second electrode comprises less than 0.1 mg/cm2 of noble metal and less than 1 weight percent of noble metal. 31. The fuel cell as claimed in claim 30, wherein the second electrode comprises no noble metal or an unavoidable trace impurity amount of noble metal. 32. The fuel cell as claimed in claim 28, wherein the second means is a means for providing hydrogen fuel to the second electrode when the fuel cell operates in the fuel cell mode. 33. The fuel cell as claimed in claim 32, comprising: a third means for providing water to the second electrode when the fuel cell operates in the electrolysis mode; a fourth means for removing oxygen generated at the first electrode when the fuel cell operates in the electrolysis mode; a fifth means for providing an oxidizer to the first electrode when the fuel cell operates in the fuel cell mode; and a sixth means for removing water from the second electrode when the fuel cell operates in the fuel cell mode. 34. The fuel cell as claimed in claim 28, wherein: the first electrode comprises at least one of LSM (lanthanum strontium manganite), LSCo (lanthanum strontium cobaltite), LCo (lanthanum cobaltite), LSF (lanthanum strontium ferrite), LSCoF (lanthanum strontium cobalt ferrite), PSM (praseodymium strontium manganite) or a combination thereof with an ionic conducting phase; and the second electrode comprises at least one of Ni, Cu, Fe or a combination thereof with an ionic conducting phase. 35. The fuel cell as claimed in claim 34, wherein: the first electrode consists essentially of LSM (lanthanum strontium manganite); and the second electrode consists essentially of a Ni-YSZ cermet. 36. A method of operating a solid oxide regenerative fuel cell, comprising: operating the solid oxide regenerative fuel cell in a fuel cell mode by providing a fuel to a negative electrode and providing an oxidizer to a positive electrode to generate electricity and water vapor at the negative electrode; operating the solid oxide regenerative fuel cell in an electrolysis mode by providing electricity to the fuel cell and providing water vapor to the negative electrode to generate fuel at the negative electrode and oxygen at the positive electrode; and charcterized in that providing a sufficient reducing atmosphere to the negative electrode when the solid oxide regenerative fuel cell operates in the electrolysis mode to prevent the negative electrode from oxidizing, wherein the negative electrode comprises less than 1 mg/cm2 of noble metal. 37. The method as claimed in claim 36, wherein the fuel and the reducing atmosphere comprise hydrogen. 38. The method as claimed in claim 37, wherein the water to hydrogen ratio at the negative electrode during the electrolysis mode is 8 or less. 39. The method as claimed in claim 36, wherein the reducing atmosphere comprises forming gas. 40. The method as claimed in claim 36, wherein the reducing atmosphere comprises carbon monoxide. 41. The method as claimed in claim 36, wherein the negative electrode comprises less than 20 weight percent of noble metal. 42. The method as claimed in claim 41, wherein the negative electrode comprises less than 0.1 mg/cm2 of noble metal and less than 1 weight percent of noble metal. 43. The method as claimed in claim 42, wherein the negative electrode comprises no noble metal or an unavoidable trace impurity amount of noble metal. 44. The method as claimed in claim 43, wherein: the positive electrode comprises at least one of LSM (lanthanum strontium manganite), LSCo (lanthanum strontium cobaltite), LCo (lanthanum cobaltite), LSF (lanthanum strontium ferrite), LSCoF (lanthanum strontium cobalt ferrite), PSM (praseodymium strontium manganite) or a combination thereof with an ionic conducting phase; and the negative electrode comprises at least one of Ni, Cu, Fe or a combination thereof with an ionic conducting phase. 45. The method as claimed in claim 44, wherein: the positive electrode consists essentially of LSM; and the negative electrode consists essentially of a Ni-YSZ cermet. 46. The method as claimed in claim 36, wherein the reducing atmosphere does not chemically participate in the electrolysis process and is cycled through the fuel cell without being consumed. 47. The method as claimed in claim 46, wherein the fuel cell is cycled between the fuel cell mode and the electrolysis mode at least 30 times. 48. The method as claimed in claim 47, comprising: generating hydrogen at the negative electrode in the electrolysis mode by electrolysis of water vapor; providing remaining water vapor and the generated hydrogen to a water- hydrogen separator to separate the hydrogen from water; providing the separated hydrogen to a compressor; providing a first portion of the compressed hydrogen to a hydrogen storage vessel; and providing a second portion of the compressed hydrogen to the negative electrode to maintain the sufficient reducing atmosphere at the negative electrode. A solid oxide regenerative fuel cell and method of operation thereof are disclosed. The solid oxide regenerative fuel cell comprises a ceramic electrolyte, a first electrode which is adapted to be positively biased when the fuel cell operates in a fuel cell mode and in an electrolysis mode, and a second electrode which is adapted to be negatively biased when the fuel cell operates in the fuel cell mode and in the electrolysis mode. The second electrode comprises less than 1 mg/cm2 of noble metal.

Full Text

A SOLID OXIDE REGENERATIVE FUEL CELL AND
METHOD OF OPERATION THEREOF
BACKGROUND OF THE INVENTION
[0001] The present invention is generally directed to a solid oxide
regenerative fuel cell and method of operation thereof and more specifically to
reversible fuel cells and their operation.
[0002] Fuel cells are electrochemical devices which can convert energy stored
in fuels to electrical energy with high efficiencies. There are classes of fuel cells that
also allow reversed operation, such that oxidized fuel can be reduced back to
unoxidized fuel using electrical energy as an input.
[0003] One type of reversible or regenerative fuel cell is the solid oxide
regenerative fuel cell (SORFC) which generates electrical energy and reactant product
from fuel and oxidizer in a fuel cell or discharge mode and which generates the fuel
and oxidant from the reactant product and the electrical energy in an electrolysis or
charge mode. The SORFC contains a ceramic electrolyte, a positive or oxygen
electrode and a negative or fuel electrode. The electrolyte may be yttria stabilized
zirconia ("YSZ") or doped ceria. The positive electrode is exposed to an oxidizer,
such as air, in the fuel cell mode and to a generated oxidant, such as oxygen gas, in
the electrolysis mode. The positive electrode may be made of a ceramic material,
such as lanthanum strontium manganite ("LSM") having a formula (La,Sr)MnO3 or
lanthanum strontium cobaltite (LSCo) having a formula (La,Sr)CoO3. The negative
electrode is exposed to a fuel, such as hydrogen gas, in a fuel cell mode and to water
vapor (i.e., reactant product) in the electrolysis mode. Since the negative electrode is
exposed to water vapor, it is made entirely of a noble metal or contains a large amount
of noble metal which does not oxidize when exposed to water vapor. For example,
the negative electrode may be made of platinum.
[0004] However, the noble metals are expensive and increase the cost of the
fuel cell. In contrast, the prior art acknowledges that the negative electrodes cannot
be made from a non-noble metal in a SORFC because such electrodes are oxidized by
the water vapor in the electrolysis mode. For example, an article by K. Eguchi et al.
in Solid State Ionics 86-88 (1996) 1245-1249 states on page 1246 that a cell with Ni-

YSZ electrodes is not suitable for a solid oxide electrolyzer cell. The article further
states on page 1247 that that a high concentration of steam (i.e., water vapor) caused
the deterioration of a Ni-YSZ electrode and that a noble or precious metal negative
electrode is preferred.
BRIEF SUMMARY OF THE INVENTION
[0005] One preferred aspect of the present invention provides a solid oxide
regenerative fuel cell, comprising a ceramic electrolyte, a first electrode which is
adapted to be positively biased when the fuel cell operates in a fuel cell mode and in
an electrolysis mode, and a second electrode which is adapted to be negatively biased
when the fuel cell operates in the fuel cell mode and in the electrolysis mode. The
second electrode comprises less than 1 mg/cm2 of noble metal.
[0006] Another preferred aspect of the present invention provides a method of
operating a solid oxide regenerative fuel cell, comprising operating the solid oxide
regenerative fuel cell in a fuel cell mode by providing a fuel to a negative electrode
and providing an oxidizer to a positive electrode to generate electricity and water
vapor at the negative electrode. The method further comprises operating the solid
oxide regenerative fuel cell in an electrolysis mode by providing electricity to the fuel
cell and providing water vapor to the negative electrode to generate fuel at the
negative electrode and oxygen at the positive electrode. The method further
comprises providing a sufficient reducing atmosphere to the negative electrode when
the solid oxide regenerative fuel cell operates in the electrolysis mode to prevent the
negative electrode from oxidizing. The negative electrode comprises less than 1
mg/cm2 of noble metal.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[0007] Figure 1 is a schematic illustration of a SORFC system operating in an
electrolysis mode according to a preferred embodiment of the present invention.
[0008] Figure 2 is a schematic illustration of a SORFC system operating in a
fuel cell mode according to a preferred embodiment of the present invention.

[0009] Figure 3 is a schematic cross section of a single SORFC operating in
the electrolysis mode according to a preferred embodiment of the present invention.
[0010] Figure 4 is a schematic cross section of a single SORFC operating in
the fuel cell mode according to a preferred embodiment of the present invention.
[0011] Figure 5 is a plot of current potential and power density versus current
density of a SORFC cell according to a specific example of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0012] The present inventors have realized that SORFC negative (i.e., fuel)
electrode may contain no noble metals or a small amount of noble metals, such as
less than 1 mg/cm2 of noble metal, if a sufficient reducing atmosphere is provided to
the negative electrode when the fuel cell operates in the electrolysis mode to prevent
the negative electrode from oxidizing. The use of cheaper and/or more common
conductive materials in the negative electrode reduces the cost of the SORFC and
improves operational performance.
[0013] As used herein, the term noble metal includes gold, iridium, palladium,
platinum, rhodium, osmium and silver. These metals are also known as precious
metals. Preferably, the negative electrode contains less than 20 weight percent of
noble metal. More preferably, the negative electrode contains less than 0.1 mg/cm2 of
noble metal and less than 1 weight percent of noble metal. Most preferably, the
negative electrode contains no noble metal or an unavoidable trace impurity amount
of noble metal. Furthermore, it is preferred that the positive electrode also contains
no noble metal or an unavoidable trace impurity amount of noble metal.
[0014] As used herein, the term SORFC (i.e., solid oxide regenerative fuel
cell) includes a ceramic electrolyte, a positive or oxygen electrode which is adapted to
be positively biased when the fuel cell operates in a fuel cell mode and in an
electrolysis mode, and a negative or fuel electrode which is adapted to be negatively
biased when the fuel cell operates in the fuel cell mode and in the electrolysis mode.
Oxygen ions are conducted, through the ceramic electrolyte from the positive

electrode to the negative electrode when the fuel cell operates in the fuel cell mode
and from the negative electrode to the positive electrode when the fuel cell operates in
the electrolysis mode.
[0015] Any suitable materials may be used for the electrolyte and the
electrodes. For example, the negative electrode may comprise a non-noble metal,
such as at least one of Ni, Cu, Fe or a combination thereof with an ionic conducting
phase (i.e., a cermet). In one preferred aspect of the invention, the negative electrode
consists essentially of a Ni-YSZ cermet (i.e., a nickel-yttria stabilized zirconia
cermet). Any suitable weight ratio of nickel to YSZ may be used in the electrode,
such as a ratio of 30:70 to 95:5, preferably 65:35. The electrolyte may comprise any
suitable ceramic, such as YSZ and/or doped ceria.
[0016] In another preferred aspect of the invention, the negative electrode
consists essentially of a Ni-doped ceria cermet. Any suitable weight ratio of nickel to
doped ceria may be used in the electrode, such as a ratio of 30:70 to 95:5, preferably
65:35. In this case, the electrolyte preferably comprises a doped ceria electrolyte or a
combination electrolyte having a doped ceria portion or layer in contact with the
negative electrode and a YSZ portion in contact with the positive electrode. The ceria
may be doped with any suitable dopant, such as a Sc dopant or a rare earth dopant
selected from Gd and Sm, in an amount sufficient to render the ceria to be ionically
conducting.
[0017] The positive electrode may comprise any suitable material. Preferably,
the positive electrode comprises a conductive perovskite ceramic material selected
from LSM, LSCo, LCo, LSF, LSCoF, PSM or a combination thereof with an ionic
conducting phase. Lanthanum strontium manganite ("LSM") preferably has a
formula (Lax,Sr1-x) MnO3 where x ranges from 0.6 to 0.99, preferably from 0.8 to
0.85. Lanthanum strontium cobaltite ("LSCo") preferably has a formula
(Lax,Sr1-x)CoO3 where x ranges from 0.6 to 0.99, preferably 0.8 to 0.85. If x is equal
to one, then the electrode material comprises LCo. Lanthanum strontium ferrite
("LSF") preferably has a formula (Lax Sr1-x)FeO3 where x ranges from 0.4 to 0.99,
preferably from 0.6 to 0.7. Lanthanum strontium cobalt ferrite ("LSCoF") preferably

has a formula (Lax,Sr1-x)(Fey,Co1-y)O3 where x ranges from 0.4 to 0.99, preferably
from 0.6 to 0.7 and y ranges from 0.01 to 0.99, preferably from 0.7 to 0.8.
Praseodymium Strontium Manganite ("PSM") preferably has a formula
(Prx,Sr1-x)MnO3 where x ranges from 0.6 to 0.99, preferably from 0.8 to 0.85. The
perovskite electrode materials may optionally be admixed with the electrode
ceramics, such as YSZ and doped ceria, such as GDC (gadolinium doped ceria).
Other suitable pervoskite electrode materials may also be used.
[0018] As used herein, "a sufficient reducing atmosphere to prevent the
negative electrode from oxidizing" comprises any suitable reducing gas which when
mixed with water vapor provided to the negative electrode during electrolysis mode
prevents the negative electrode from oxidizing to an extent which prevents it from
operating according to its designed parameters during its expected life span, such as
for at least one month, preferably at least one year, such as one to ten years, for
example. Preferably, hydrogen is used as the reducing gas. However, other gases,
such as forming gas (a nitrogen/hydrogen mixture) and carbon monoxide may also be
used alone or in combination with hydrogen. The maximum ratio of water vapor to
reducing gas provided to the negative electrode during the electrolysis mode depends
on the material of the negative electrode and on the type of reducing gas used. Some
negative electrode materials require more reducing gas to prevent oxidation that other
negative electrode materials. For example, if a hydrogen reducing gas is used for a
Ni-YSZ electrode, then the water to hydrogen ratio is preferably 8 or less, for example
0.1 to 8, such as 0.4 to 5 or 0.44 to 1. However, the water to hydrogen ratio may be
different than the ratio provided above depending on various factors, such as the
electrode composition, the overall gas composition provided to the negative electrode
and other factors, while still preventing the negative electrode from oxidizing to an
extent which prevents it from operating according to its designed parameters during
its expected life span. Preferably, the reducing atmosphere (i.e., the reducing gas)
does not chemically participate in the electrolysis process and is cycled through the
fuel cell without being consumed.

[0019] Figure 1 illustrates a SORFC system 1 operating in the electrolysis or
charge mode. The system 1 contains a schematically illustrated SORFC 10. While
only a single SORFC 10 is shown, it should be understood that the system 1
preferably contains a stack of SORFCs, containing a plurality of electrolytes, positive
electrodes and negative electrodes. The system 1 also contains a fuel storage vessel
101, such as a hydrogen tank, an optional fuel compressor 103, a water-hydrogen
separator / water storage device 105, a water pump 107, an oxidizer blower 109, a fuel
bleed valve 111 and optional water, oxidizer and compressor valves 113, 115 and 117,
respectively. The system 1 also contains heat exchangers 119 and 121 which preheat
the inlet streams into the fuel cell 10 using the fuel cell exhaust streams. The system
further contains fuel and oxidizer conduits, such as pipes, hoses or other suitable gas
and liquid conduits, which connect the above mentioned components together.
[0020] The system contains a reducing gas conduit 123 which provides a
sufficient reducing atmosphere to the negative electrode of the fuel cell 10 when the
fuel cell operates in the electrolysis mode to prevent the negative electrode from
oxidizing. Preferably, the reducing gas 123 conduit also comprises a fuel conduit
which is used to provide fuel to the negative electrode during the fuel cell or
discharge mode. Thus, the reducing gas in the electrolysis mode preferably, but not
necessarily, comprises the same gas as the fuel which is used in the fuel cell mode. In
the electrolysis mode, the bleed valve 111 located in the reducing gas conduit is
partially opened to provide a smaller amount of fuel/reducing gas to the fuel cell than
in the fuel cell mode.
[0021] Preferably, the reducing gas/fuel comprises hydrogen and the reducing
gas conduit 123 comprises a hydrogen conduit operatively connected to at least one of
a hydrogen compressor 103 and the hydrogen fuel storage vessel 101. The term
operatively connected means that the conduit 123 may be directly or indirectly
connected to the compressor 103 and/or vessel 101 to allow hydrogen to flow from
the compressor 103 and/or vessel 101 through the conduit 123 into the fuel cell. The
conduit 123 is operatively connected to the fuel inlet of a fuel cell 10 (i.e., to the inlet
of the fuel cell stack).

[0022] The water-hydrogen separator 105 is also operatively connected to the
fuel inlet of the fuel cell via the water inlet conduit 125. The separator 105 provides
water to the negative electrode of the fuel cell 10 when the fuel cell 10 operates in the
electrolysis mode. Preferably, the conduits 123 and 125 converge at the three way
valve 113, and inlet conduit 127 provides the water and reducing gas from valve 113
to the negative electrode of the fuel cell 10.
[0023] A fuel outlet of the fuel cell 10 is operatively connected to a water-
hydrogen separator 105 via a fuel exhaust conduit 129. Conduit 129 removes water
from the negative electrode when the fuel cell operates in the fuel cell mode. An
oxygen exhaust conduit 131 removes oxygen generated at the positive electrode when
the fuel cell operates in the electrolysis mode. An oxidizer inlet conduit 133 provides
an oxidizer, such as air or oxygen, to the positive electrode of the fuel cell 10 when
the fuel cell operates in the fuel cell mode. In the electrolysis mode, the conduit 133
is closed by valve 115.
[0024] Figure 2 illustrates the SORFC system 1 operating in the fuel cell or
discharge mode. The system 1 is the same, except that the bleed valve 111 is opened
to a greater amount than in the electrolysis mode, the oxidizer valve 115 is open
instead of closed and the water valve 113 either totally or partially closes the water
conduit 125.
[0025] A method of operating the solid oxide regenerative fuel cell system 1
will now be described. In the fuel cell mode shown in Figure 2, a fuel, such as
hydrogen, carbon monoxide and/or a hydrocarbon gas, such as methane, is provided
to the negative electrode of the fuel cell 10 from storage vessel 101 through conduits
123 and 127. The fuel is preheated in the heat exchanger 119. If desired, some water
from the separator/storage device 105 is provided via conduits 125 and 127 to the
negative electrode of the fuel cell as well. Alternatively, the water may be provided
from a water pipe rather than from storage.
[0026] An oxidizer, such as oxygen or air is provided to the positive electrode
of the fuel cell 10 through conduit 133. This generates electricity (i.e., electrical

energy) and water vapor at the negative electrode. The unused oxidizer is discharged
through conduit 131. The water vapor reactant product along with unused fuel, such
as hydrogen, and other gases, such as carbon monoxide, are discharged from the fuel
cell through conduit 129 into the separator 105. The hydrogen is separated from
water in the separator and is provided into the compressor 103 through conduit 135.
The compressor 103 cycles the hydrogen back into the fuel cell 10.
[0027] In the electrolysis mode shown in Figure 1, electricity is provided to
the fuel cell. Water vapor is provided to the negative electrode of the fuel cell 10
from the separator/storage device 105 or from a water pipe through conduits 125 and
127. A sufficient reducing atmosphere, such as hydrogen gas, is also provided to the
negative electrode through conduits 123 and 127. For example, at start-up of the
SORFC operation, when the compressor 103 does not usually run, the hydrogen may
be provided from the storage vessel 101. Subsequently, when the compressor 103
becomes operational at steady state, it provides hydrogen to the conduit 123 and to the
storage vessel 101.
[0028] This generates fuel, such as hydrogen, at the negative electrode, and
oxygen at the positive electrode of the fuel cell. The hydrogen, including the
hydrogen generated in the electrolysis of water vapor reaction and the hydrogen
provided from conduit 123 along with remaining unreacted water vapor are provided
from the fuel cell 10 through conduit 129 to the separator 105. The water-hydrogen
separator 105 separates the hydrogen from water, with the water being either stored or
discharged. The separated hydrogen is provided to the compressor 103 through
conduit 135. The compressor provides a first portion of the compressed hydrogen to
the hydrogen storage vessel 101 and provides a second portion of the compressed
hydrogen to the negative electrode of the fuel cell 10 through conduit 125 to maintain
the sufficient reducing atmosphere at the negative electrode. The oxygen generated
during the electrolysis reaction is discharged through conduit 131.
[0029] Preferably, the fuel cell 10 is cycled between the fuel cell mode and the
electrolysis mode at least 30 times, such as 30 to 3,000 times. During the cycles,
when the fuel cell operates in the electrolysis mode, the bleed valve 111 bleeds a first

sufficient amount of hydrogen from at least one of the hydrogen compressor and the
hydrogen fuel storage vessel through the hydrogen conduit 123 to the negative
electrode of the fuel cell to prevent the negative electrode from oxidizing. Providing
a reducing atmosphere on the negative electrode during the electrolysis mode allows
the use of non-noble materials in the electrode which also maintains compatibility for
the electrolysis operation.
[0030] When the fuel cell operates in the fuel cell mode, the bleed valve
provides hydrogen fuel from, the hydrogen storage vessel through the hydrogen
conduit 123 to the negative electrode in a second amount greater than the first
amount. In other words, the first amount of reducing gas should be a small amount of
reducing gas, but sufficient to prevent oxidation of the negative electrode.
[0031] It should be noted that the hydrogen conduit 123 provides a sufficient
amount of reducing gas to the plurality of negative electrodes of a fuel cell stack to
prevent all negative electrodes of the stack from oxidizing. Therefore the negative
electrodes of the SORFC stack are maintained in a reducing atmosphere, preventing
oxidation of the electrode materials at elevated temperatures in the range 600-1000°C.
[0032] In alternative embodiments of the present invention, separate storage
vessels are used to store fuel and the reducing gas. Preferably, this occurs when the
fuel and reducing gas comprise different gases. For example, the fuel may comprise a
hydrocarbon fuel rather than hydrogen, or forming gas or carbon monoxide is used as
a reducing gas. In this case, a separate reducing gas storage vessel, such as a
hydrogen, carbon monoxide or forming gas storage tank or pipe may be used to
provide the reducing gas into the fuel cell 10 in the electrolysis mode, while the fuel
storage vessel 101 is used to provide fuel into the fuel cell in the fuel cell mode.
[0033] A single SORFC 10 operating in the electrolysis mode is shown in
Figure 3. The SORFC contains an anode (positive) electrode 11, an electrolyte 13 and
a cathode (negative) electrode 12. An anode gas chamber 14 is formed between the
electrolyte 13 and an anode side interconnect (not shown for simplicity). A cathode

gas chamber 15 is formed between the electrolyte 13 and a cathode side interconnect
(also not shown for simplicity).
[0034] A reaction product gas mixture 17 may contain primarily water with
reducing gas, such as hydrogen. Alternatively, the reaction product gas mixture 17
may contain primarily water vapor and carbon dioxide if a carbon containing gas or
liquid, such as methane, is used as a fuel. Hydrogen, carbon monoxide or forming gas
is also added to the gas mixture as the reducing gas.
[0035] The reaction product gas mixture 17 is introduced into the cathode gas
chamber 15. A direct current power source (not shown) is connected to the anode
electrode 11 and the cathode electrode 12 in such a way that when electrical current is
flowing, the anode electrode 11 takes on a positive voltage charge and the cathode
electrode 12 takes on a negative voltage charge. When the electric current is flowing,
the gas mixture 17 gives up oxygen ions 16 to form cathode discharge mixture 19
consisting primarily of hydrogen and optionally carbon monoxide if mixture 17
contained carbon dioxide. Oxygen ions 16 transport across the electrolyte 13 under
the electrical current. The oxygen ions 16 are converted into the oxidant, such as
oxygen gas 18 on the anode electrode 11 under the influence of the electrical current.
The oxygen gas 18 is discharged from the anode chamber 14, while the electrolysis
product (e.g., hydrogen and optionally carbon monoxide) is collected from the
cathode chamber. If carbon monoxide is present in the product, then the product may
be converted to methane fuel and water in a Sabatier reactor.
[0036] A single SORFC 20 operating in the fuel cell mode is shown in Fig. 4.
SORFC 20 is the same as SORFC 10, except that the cathode and anode designations
of its electrodes are reversed. Cathode (positive) electrode 21 is the same electrode as
that identified as the anode (positive) electrode 11 in Fig. 3 when operating in the
electrolysis mode. Anode (negative) electrode 22 is the same electrode as that
identified as the cathode (negative) electrode 12 in Fig. 3 when operating in the
electrolysis mode. Solid oxide electrolyte 23 is the same electrolyte as that identified
as electrolyte 13 in Fig. 4 when operating in the electrolysis mode. Cathode gas
chamber 24 is the same gas chamber as that identified as the "anode gas chamber 14 in

Fig. 3 when operating in the electrolysis mode. Anode gas chamber 25 is the same
gas chamber as that identified as the cathode gas chamber 15 in Fig. 3 when operating
in the electrolysis mode.
[0037] A fuel gas 27 is introduced into the anode gas chamber 25. An
oxidizer, such as air or oxygen gas 28 is introduced into the cathode chamber 24. The
fuel may comprise hydrogen, a hydrocarbon gas, such as methane, and/or carbon
monoxide. Water may be added to the fuel if desired. An electrical fuel cell load (not
shown) is applied to the SORFC 20 and the oxygen gas 28 forms oxygen ions 26
under the influence of the electrical load. Oxygen ions 26 transport across the
electrolyte 23 under the influence of the electrical current. On the anode electrode 22,
the oxygen ions 26 combine with hydrogen and optionally carbon, if present, from gas
mixture 27 to form gas mixture 29 containing water vapor and optionally carbon
dioxide, if a carbon containing gas is present in the fuel 27. Gas mixture 29 is
discharged from the anode chamber and stored as the reaction product. In the process
described above, the SORFC 20 has made electrical energy or power, which is output
through its electrodes.
[0038] The SORFC systems described herein may have other embodiments
and configurations, as desired. Other components, such as fuel side exhaust stream
condensers, heat exchangers, heat-driven heat pumps, turbines, additional gas
separation devices, hydrogen separators which separate hydrogen from the fuel
exhaust and provide hydrogen for external use, fuel preprocessing subsystems, fuel
reformers, water-gas shift reactors, and Sabatier reactors which form methane from
hydrogen and carbon monoxide, may be added if desired, as described, for example,
in U.S. Application Serial Number 10/300,021, filed on November 20, 2002, in U.S.
Provisional Application Serial Number 60/461,190, filed on April 9 2003, and in U.S.
Application Serial Number 10/446,704, filed on May 29, 2003 all incorporated herein
by reference in their entirety.
[0039] The following specific example is provided for illustration only and
should not be considered limiting on the scope of the present invention. Figure 5
illustrates the plot of cell potential and power density versus current density for a

single 10 cm2 SORFC cell using a test bed that models the inlet gas streams as
described with respect to Figures 1 and 2 above. The SORFC cell contains the
following components. The negative or fuel electrode is a Ni-YSZ cermet electrode
containing 65 weight percent Ni and 35 weight percent YSZ. This electrode is 27
microns thick and is made by screen printing on the electrolyte and being fired to
1350°C. The electrolyte is a YSZ electrolyte that is 300 microns thick. The
electrolyte is tape cast and fired to 1550°C. The positive or oxygen electrode is an
LSM electrode that is 39 microns thick. This electrode is made by screen printing on
the electrolyte and firing to 1200°C.
[0040] The negative electrode is fed with a constant 300 seem of H2 passing
through a humidifier at a set temperature. The charge (i.e., electrolysis) mode is run
with the humidifier set to 70°C or 30.75% H2O. This provides an H2O to H2 ratio of
0.44 to the negative electrode. One discharge (i.e., fuel cell) mode is run with the
humidifier set to 70°C or 30.75% H2O, while another discharge (i.e., fuel cell) mode
is run with the humidifier set to 29°C or 3.95% H2O. The H2O to H2 ratio is 0.44 and
0.04, respectively, for the respective discharge mode runs. Table 1 below lists the
negative electrode conditions for the various modes of operation with ambient
pressure reactants.

[0041] As shown in Figure 5, this fuel cell with a negative electrode which
contains no noble metal is successfully operated in both charge and discharge modes
and exhibits acceptable current-voltage and current-power characteristics for
reversible operation.

[0042] The foregoing description of the invention has been presented for
purposes of illustration and description. It is not intended to be exhaustive or to limit
the invention to the precise form disclosed, and modifications and variations are
possible in light of the above teachings or may be acquired from practice of the
invention. The description was chosen in order to explain the principles of the
invention and its practical application. It is intended that the scope of the invention be
defined by the claims appended hereto, and their equivalents.

WE CLAIM:
1. A solid oxide regenerative fuel cell, comprising:
a ceramic electrolyte;
a first electrode which is adapted to be positively biased when the fuel cell
operates in a fuel cell mode and in an electrolysis mode; and
a second electrode which is adapted to be negatively biased when the fuel cell
operates in the fuel cell mode and in the electrolysis mode, characterized in that:
the second electrode comprises less than 1 mg/cm2 of noble metal.
2. The fuel cell as claimed in claim 1, wherein the second electrode comprises
less than 20 weight percent of noble metal.
3. The fuel cell as claimed in claim 2, wherein the second electrode comprises
less than 0.1mg/cm2 of noble metal and less than 1 weight percent of noble metal.
4. The fuel cell as claimed in claim 3, wherein the second electrode comprises no
noble metal or an unavoidable trace impurity amount of noble metal.
5. The fuel cell as claimed in claim 3, comprising a first device which is adapted
to provide a sufficient reducing atmosphere to the second electrode when the fuel cell
operates in the electrolysis mode to prevent the second electrode from oxidizing.
6. The fuel cell as claimed in claim 5, wherein the first device comprises a
hydrogen conduit operatively connected to at least one of a hydrogen compressor and
a hydrogen fuel storage vessel.
7. The fuel cell as claimed in claim 6, wherein the hydrogen conduit is
operatively connected to a fuel inlet of a fuel cell stack and a fuel outlet of the fuel
cell stack is operatively connected to a water-hydrogen separator.

8. The fuel cell as claimed in claim 7, wherein the water-hydrogen separator is
operatively connected to the fuel inlet of the fuel cell stack and is adapted to provide
water to the second electrode when the fuel cell operates in the electrolysis mode.
9. The fuel cell as claimed in claim 6, comprising a valve which is adapted to
bleed a first sufficient amount of hydrogen from at least one of the hydrogen
compressor and the hydrogen fuel storage vessel through the hydrogen conduit to the
second electrode to prevent the second electrode from oxidizing when the fuel cell
operates in the electrolysis mode and which is adapted to provide hydrogen fuel from
the hydrogen storage vessel through the hydrogen conduit to the second electrode in a
second amount greater than the first amount when the fuel cell operates in the fuel cell
mode.
10. The fuel cell as claimed in claim 6, wherein the first device comprises a
forming gas conduit operatively connected to a forming gas storage vessel.
11. The fuel cell as claimed in claim 6, wherein the first device comprises a
carbon monoxide conduit operatively connected to a carbon monoxide storage vessel.
12. The fuel cell as claimed in claim 1, comprising a first means for providing a
sufficient reducing atmosphere to the second electrode when the fuel cell operates in
the electrolysis mode to prevent the second electrode from oxidizing.
13. The fuel cell as claimed in claim 12, wherein the first means is a means for
providing hydrogen fuel to the second electrode when the fuel cell operates in the fuel
cell mode.
14. The fuel cell as claimed in claim 13, comprising:
a second means for providing water to the second electrode when the fuel cell
operates in the electrolysis mode;

a third means for removing oxygen generated at the first electrode when the
fuel cell operates in the electrolysis mode;
a fourth means for providing an oxidizer to the first electrode when the fuel
cell operates in the fuel cell mode; and
a fifth means for removing water from the second electrode when the fuel cell
operates in the fuel cell mode.
15. The fuel cell as claimed in claim 5, wherein the second electrode comprises at
least one of Ni, Cu, Fe or a combination thereof with an ionic conducting phase.
16. The fuel cell as claimed in claim 15, wherein the second electrode consists
essentially of a Ni-YSZ cermet.
17. The fuel cell as claimed in claim 15, wherein:
the second electrode consists essentially of a Ni-doped ceria cermet; and
the electrolyte comprises a doped ceria portion in contact with the second
electrode and a YSZ portion in contact with the first electrode.
18. The fuel cell as claimed in claim 15, wherein:
the electrolyte comprises YSZ, doped ceria or a combination thereof; and
the first electrode comprises at least one of LSM (lanthanum strontium
manganite), LSCo (lanthanum strontium cobaltite), LCo (lanthanum cobaltite), LSF
(lanthanum strontium ferrite), LSCoF (lanthanum strontium cobalt ferrite), PSM
(praseodymium strontium manganite) or a combination thereof with an ionic
conducting phase.
19. A solid oxide regenerative fuel cell, comprising:
a first electrode which is adapted to be positively biased when the fuel cell
operates in a fuel cell mode and in an electrolysis mode;

a second electrode which is adapted to be negatively biased when the fuel cell
operates in the fuel cell mode and in the electrolysis mode, characterized in that the
second electrode comprises less than 1 mg/cm2 of noble metal; and
a first means such as herein described for conducting oxygen ions from the
first electrode to the second electrode when the fuel cell operates in the fuel cell mode
and for conducting oxygen ions from the second electrode to the first electrode when
the fuel cell operates in the electrolysis mode.
20. The fuel cell as claimed in claim 19, wherein the second electrode comprises
less than 20 weight percent of noble metal.
21. The fuel cell as claimed in claim 20, wherein the second electrode comprises
less than 0.1 mg/cm2 of noble metal and less than 1 weight percent of noble metal.
22. The fuel cell as claimed in claim 21, wherein the second electrode comprises
no noble metal or an unavoidable trace impurity amount of noble metal.
23. The fuel cell as claimed in claim 19, comprising a second means such as
herein described for providing a sufficient reducing atmosphere to the second
electrode when the fuel cell operates in the electrolysis mode to prevent the second
electrode from oxidizing.
24. The fuel cell as claimed in claim 23, wherein the second means is a means for
providing hydrogen fuel to the second electrode when the fuel cell operates in the fuel
cell mode.
25. The fuel cell as claimed in claim 24, comprising:
a third means such as herein described for providing water to the second
electrode when the fuel cell operates in the electrolysis mode;
a fourth means such as herein described for removing oxygen generated at the
first electrode when the fuel cell operates in the electrolysis mode;

a fifth means such as herein described for providing an oxidizer to the first
electrode when the fuel cell operates in the fuel cell mode; and
a sixth means such as herein described for removing water from the second
electrode when the fuel cell operates in the fuel cell mode.
26. The fuel cell as claimed in claim 19, wherein:
the first electrode comprises at least one of LSM, LSCo, LCo, LSF, LSCoF,
PSM or a combination thereof with an ionic conducting phase; and
the second electrode comprises at least one of Ni, Cu, Fe or a combination
thereof with an ionic conducting phase.
27. The fuel cell as claimed in claim 26, wherein:
the first electrode consists essentially of LSM; and
the second electrode consists essentially of a Ni-YSZ cermet.
28. A solid oxide regenerative fuel cell, comprising:
a first electrode which is adapted to be positively biased when the fuel cell
operates in a fuel cell mode and in an electrolysis mode;
a second electrode which is adapted to be negatively biased when the fuel cell
operates in the fuel cell mode and in the electrolysis mode, characterized in that the
second electrode comprises less than 1 mg/cm2 of noble metal;
a first means such as herein described such as herein described for conducting
oxygen ions from the first electrode to the second electrode when the fuel cell
operates in the fuel cell mode and for conducting oxygen ions from the second
electrode to the first electrode when the fuel cell operates in the electrolysis mode;
and
a second means such as herein described for providing a sufficient reducing
atmosphere to the second electrode when the fuel cell operates in the electrolysis
mode to prevent the second electrode from oxidizing.

29. The fuel cell as claimed in claim 28, wherein the second electrode comprises
less than 20 weight percent of noble metal.
30. The fuel cell as claimed in claim 29, wherein the second electrode comprises
less than 0.1 mg/cm2 of noble metal and less than 1 weight percent of noble metal.
31. The fuel cell as claimed in claim 30, wherein the second electrode comprises
no noble metal or an unavoidable trace impurity amount of noble metal.
32. The fuel cell as claimed in claim 28, wherein the second means is a means for
providing hydrogen fuel to the second electrode when the fuel cell operates in the fuel
cell mode.
33. The fuel cell as claimed in claim 32, comprising:
a third means for providing water to the second electrode when the fuel cell
operates in the electrolysis mode;
a fourth means for removing oxygen generated at the first electrode when the
fuel cell operates in the electrolysis mode;
a fifth means for providing an oxidizer to the first electrode when the fuel cell
operates in the fuel cell mode; and
a sixth means for removing water from the second electrode when the fuel cell
operates in the fuel cell mode.
34. The fuel cell as claimed in claim 28, wherein:
the first electrode comprises at least one of LSM (lanthanum strontium
manganite), LSCo (lanthanum strontium cobaltite), LCo (lanthanum cobaltite), LSF
(lanthanum strontium ferrite), LSCoF (lanthanum strontium cobalt ferrite), PSM
(praseodymium strontium manganite) or a combination thereof with an ionic
conducting phase; and

the second electrode comprises at least one of Ni, Cu, Fe or a combination
thereof with an ionic conducting phase.
35. The fuel cell as claimed in claim 34, wherein:
the first electrode consists essentially of LSM (lanthanum strontium
manganite); and
the second electrode consists essentially of a Ni-YSZ cermet.
36. A method of operating a solid oxide regenerative fuel cell, comprising:
operating the solid oxide regenerative fuel cell in a fuel cell mode by
providing a fuel to a negative electrode and providing an oxidizer to a positive
electrode to generate electricity and water vapor at the negative electrode;
operating the solid oxide regenerative fuel cell in an electrolysis mode by
providing electricity to the fuel cell and providing water vapor to the negative
electrode to generate fuel at the negative electrode and oxygen at the positive
electrode; and charcterized in that
providing a sufficient reducing atmosphere to the negative electrode when the
solid oxide regenerative fuel cell operates in the electrolysis mode to prevent the
negative electrode from oxidizing, wherein the negative electrode comprises less than
1 mg/cm2 of noble metal.
37. The method as claimed in claim 36, wherein the fuel and the reducing
atmosphere comprise hydrogen.
38. The method as claimed in claim 37, wherein the water to hydrogen ratio at the
negative electrode during the electrolysis mode is 8 or less.
39. The method as claimed in claim 36, wherein the reducing atmosphere
comprises forming gas.

40. The method as claimed in claim 36, wherein the reducing atmosphere
comprises carbon monoxide.
41. The method as claimed in claim 36, wherein the negative electrode comprises
less than 20 weight percent of noble metal.
42. The method as claimed in claim 41, wherein the negative electrode comprises
less than 0.1 mg/cm2 of noble metal and less than 1 weight percent of noble metal.
43. The method as claimed in claim 42, wherein the negative electrode comprises
no noble metal or an unavoidable trace impurity amount of noble metal.
44. The method as claimed in claim 43, wherein:
the positive electrode comprises at least one of LSM (lanthanum strontium
manganite), LSCo (lanthanum strontium cobaltite), LCo (lanthanum cobaltite), LSF
(lanthanum strontium ferrite), LSCoF (lanthanum strontium cobalt ferrite), PSM
(praseodymium strontium manganite) or a combination thereof with an ionic
conducting phase; and
the negative electrode comprises at least one of Ni, Cu, Fe or a combination
thereof with an ionic conducting phase.
45. The method as claimed in claim 44, wherein:
the positive electrode consists essentially of LSM; and
the negative electrode consists essentially of a Ni-YSZ cermet.
46. The method as claimed in claim 36, wherein the reducing atmosphere does not
chemically participate in the electrolysis process and is cycled through the fuel cell
without being consumed.

47. The method as claimed in claim 46, wherein the fuel cell is cycled between the
fuel cell mode and the electrolysis mode at least 30 times.
48. The method as claimed in claim 47, comprising:
generating hydrogen at the negative electrode in the electrolysis mode by
electrolysis of water vapor;
providing remaining water vapor and the generated hydrogen to a water-
hydrogen separator to separate the hydrogen from water;
providing the separated hydrogen to a compressor;
providing a first portion of the compressed hydrogen to a hydrogen storage
vessel; and
providing a second portion of the compressed hydrogen to the negative
electrode to maintain the sufficient reducing atmosphere at the negative electrode.

A solid oxide regenerative fuel cell and method of operation thereof are
disclosed. The solid oxide regenerative fuel cell comprises a ceramic electrolyte, a
first electrode which is adapted to be positively biased when the fuel cell operates in a
fuel cell mode and in an electrolysis mode, and a second electrode which is adapted to
be negatively biased when the fuel cell operates in the fuel cell mode and in the
electrolysis mode. The second electrode comprises less than 1 mg/cm2 of noble metal.

Documents:

692-KOLNP-2006-CORRESPONDENCE.pdf

692-KOLNP-2006-FORM 27 1.1.pdf

692-KOLNP-2006-FORM 27.pdf

692-KOLNP-2006-FORM-27.pdf

692-kolnp-2006-granted-abstract.pdf

692-kolnp-2006-granted-assignment.pdf

692-kolnp-2006-granted-claims.pdf

692-kolnp-2006-granted-correspondence.pdf

692-kolnp-2006-granted-description (complete).pdf

692-kolnp-2006-granted-drawings.pdf

692-kolnp-2006-granted-examination report.pdf

692-kolnp-2006-granted-form 1.pdf

692-kolnp-2006-granted-form 13.pdf

692-kolnp-2006-granted-form 18.pdf

692-kolnp-2006-granted-form 3.pdf

692-kolnp-2006-granted-form 5.pdf

692-kolnp-2006-granted-gpa.pdf

692-kolnp-2006-granted-reply to examination report.pdf

692-kolnp-2006-granted-specification.pdf

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Patent Number

226485

Indian Patent Application Number

692/KOLNP/2006

PG Journal Number

51/2008

Publication Date

19-Dec-2008

Grant Date

17-Dec-2008

Date of Filing

23-Mar-2006

Name of Patentee

BLOOM ENERGY CORPORATION

Applicant Address

1252, ORLEANS DRIVE, SUNNYVALE, CALIFORNIA

Inventors:

#	Inventor's Name	Inventor's Address
1	HICKEY, DARREN	210, COLLEGE AVENUE, PALO ALTO, CALIFORNIA 94306
2	RUSSELL, IAN	684, TORREYA AVENUE, SUNNYVALE, CALIFORNIA 94086

PCT International Classification Number

H02J

PCT International Application Number

PCT/US2004/029458

PCT International Filing date

2004-09-10

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	10/658,275	2003-09-10	U.S.A.